M4V to AU Converter

M4V to AU Converter

M4V is Apple's MP4 variant — an MPEG-4 container holding H.264 video and AAC audio, used by iTunes, Apple TV, and QuickTime. AU is something far older: the Sun Microsystems audio format from the late 1980s, a flat big-endian file that early Java and Unix audio pipelines read natively. This converter discards the M4V picture, decodes its AAC soundtrack, and writes the samples into an AU file.

M4V Format at a Glance

AU Format at a Glance

What This Conversion Actually Does

The M4V soundtrack is AAC, which is already lossy — perceptual data was discarded when the file was first encoded. This tool decodes that AAC and writes the result into AU, where the default encoding is uncompressed 16-bit big-endian PCM (pcm_s16be, matching AU's big-endian origin). That makes the AU file larger than the audio inside the M4V, but it cannot restore detail the original AAC threw away — you get a faithful, bulky copy of already-lossy audio, not new fidelity. The Lowest quality preset instead writes 8-bit μ-law, AU's original telephony encoding, producing a much smaller file. The video picture is dropped entirely; the output is audio only.

AU is an old Unix/Sun/NeXT/Java format, not a modern general-purpose choice. Reach for it when something specifically asks for .au: legacy Unix audio pipelines, Java AudioClip resources, telephony prompts, or DSP coursework that distributes reference clips as .au. For anything else, a small shareable file is better served by M4V to MP3, and keeping the AAC as-is without re-encoding by M4V to M4A.

How to Convert M4V to AU

1. Upload Your M4V File: Drag and drop or click "Add Files" to select M4V (or MP4) videos. Batch is supported — queue several clips and they convert sequentially.
2. Pick a Quality Preset: The default is Very High (Recommended), which writes 16-bit PCM. Choose Highest for 24/32-bit PCM archival, or Lowest for telephony-style 8-bit μ-law output.
3. Set Audio Sample Rate and Channel (Optional): Audio Sample Rate accepts Original, 8000, 12000, 16000, 24000, 44100, or 48000 Hz; Audio Channel accepts Original, Mono, or Stereo. For Java AudioClip or phone-system output, set 8000 Hz and Mono.
4. Trim and Convert: Use Trim to set a start time and duration to grab one segment instead of the whole track, then click Convert. Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically a few hours after conversion — no sign-up, no watermark.

Frequently Asked Questions

Can I extract audio from a DRM-protected iTunes M4V?

No. M4V files bought from the iTunes Store carry Apple FairPlay DRM, and no third-party converter can decode them — the encryption is tied to your Apple account and authorized devices. Only DRM-free M4V works here: files you exported from iMovie, Final Cut, QuickTime, or any non-purchased source. If the upload fails or produces silence, FairPlay is the usual reason. To use purchased content you would first need to play it back through an authorized Apple app.

Why is my AU file bigger than the M4V's audio if there's no video?

Because the M4V's audio is AAC — a compressed lossy codec at roughly 96–192 kbps — and the default AU output is uncompressed 16-bit PCM, which runs about 1.4 Mbps for stereo 44.1 kHz. So a one-minute AAC track decodes into a roughly 10 MB PCM-in-AU file. The extra bytes do not add fidelity; they are an uncompressed copy of audio that already lost detail during AAC encoding. Pick the Lowest preset at 8000 Hz mono for an AU that is actually smaller (8-bit μ-law, about 480 KB per minute).

Which AU encoding does the output use — μ-law or PCM?

By default, 16-bit big-endian linear PCM (pcm_s16be), which matches AU's big-endian heritage and suits music or general audio. The Lowest quality preset switches to 8-bit μ-law at 8000 Hz — AU's original encoding and the most universally readable, ideal for Java applets, telephony prompts, or any system that expects classic "Sun audio." The AU header records which encoding was used, so both are valid .au files.

Why is AU big-endian when most modern audio formats are little-endian?

Sun's SPARC and NeXT's Motorola 68k workstations were both big-endian processors, so the format was specified that way in the late 1980s to match native CPU memory layout. Modern x86 and ARM machines are little-endian, so their audio libraries byte-swap AU samples transparently on read. It is only an issue in low-level C that parses the header by hand, where you may need ntohl or a byte-swap intrinsic. In our testing, a one-minute stereo M4V soundtrack decoded to AU at the default Very High preset produced a roughly 10 MB 16-bit PCM .au, while the Lowest μ-law preset at 8000 Hz mono produced about 480 KB.

Is AU still worth using in 2026, or should I pick something else?

For a brand-new project, pick WAV, FLAC, or MP3 — AU is niche today. But it survives where it is specifically required: Java audio APIs still ship .au support in the JDK, older telephony stacks expect 8 kHz μ-law, and many DSP and CS courses distribute reference clips as .au because the 24-byte header is short enough to parse by hand. If a tool, textbook, or vendor asks for "AU" or "Sun audio," this conversion is the way to feed a modern M4V recording into it. If you only need a small, broadly playable file, M4V to MP3 is the better target.

How are my files handled, and how long are they kept?

Files are uploaded over an encrypted connection and processed on our servers. They are deleted automatically a few hours after conversion, and are never shared or made public. There is no sign-up and no watermark on the output. The practical limit on big videos is upload time, since the decode and re-encode happen on our servers rather than on your device.